Duo-mode wave energy feed



Sept. 23, 1958 R. s. ELLIOTT DUO-MODE WAVE ENERGY FEED .2 Sheets-Sheet 1 Filed Sept. 4, 1956 Robert 8. Elliott,

INVENTOR ATTORNE).

i ly Sept. 23, 1958 v R. s. ELLIOTT 2,853,685

DUO-MODE WAVE ENERGY FEED Filed Sept. 4, 1956 2 Sheets-Sheet 2 Robert 8. Elliott,

IIVVE/VTOR.

United States Patent DUO-MODE WAVE ENERGY FEED Robert S. Elliott, Los Angeles, Calif., assiguor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application September 4, 1956, Serial No. 607,641

6 Claims. (Cl. 333-21) This invention relates to duo-mode wave energy feeds and more particularly to a wave energy transducer which provides wave energy in a combination of the principal TEM-mode and the TE -mode of the coaxial waveguide.

In certain applications, wave energy antennas may be called upon to radiate an elliptically polarized beam of wave energy. Such antennas need be adapted to both receive and radiate wave energy polarized in two mutually perpendicular planes, and require feed means capable of exciting wave energy polarized in two mutually perpendicular planes. An adequate feed means is one adapted to excite Wave energy in two modes having their respective electric field vector at right angles to one another.

An example of an antenna adapted to radiate and receive elliptically polarized wave energy is an omnidirectional surface wave beacon antenna having a dielectric clad metallic surface. To utilize the properties of this antenna, a coaxial waveguide feed is used to supply the dielectric trapping agent with elliptically polarized wave energy of high power. One way to obtain the desired cross components of wave energy is to excite wave energy in the coaxial feed waveguide in two modes, namely the TEM-mode and the TE -mode.

It is therefore an object of this invention to provide a wave energy feed which is adapted to excite-wave energy in a combination of the TEM-mode and the TE -mode of a coaxial waveguide at its output end.

It is a further object of this invention to provide a device which, upon being excited, wave energy in the dominant TE -mode of the rectangular Waveguide trans forms the excited mode into the TE -mode of a coaxial waveguide and intermixes the wave energy in the transformed mode with wave energy in the TEM-mode of the coaxial waveguide.

It is a still further object of this invention to provide a new and novel duo-mode feed waveguide capable of providing wave energy in a combination of substantially pure TEM and TE -modes of the coaxial waveguide without the employment of interposed excitation elements which feed waveguide is simple in operation and capable of handling large amounts of power.

In accordance with this invention, a duo-mode wave energy feed having two input and one output terminal couples a rectangular input waveguide adapted to propagate wave energy in the dominant TE -mode and a coaxial input waveguide adapted to propagate wave energy in the principal TEM-mode to a coaxial output Waveguide adapted to 'propagatewave energy in the duo-mode comprising the combination of the TEM-mode and the TE -mode. The duo-mode waveguide feed of this invention has a double function, namely to reorient the TE -mode of the rectangular input waveguide in progressive incremental stages until the electric field of the TE mode of the coaxial output waveguides is obtained and thereafter to intermix the TE-mode and the TEM-mode of the coaxial input waveguide without generating higher order modet,

The TE -mode of the rectangular input waveguide is transformed by the duo-mode wave energy feed to the TE -mode of the coaxial output waveguide by first dividing the wave energy in the dominantTE -mode into two portions of equal amplitude having their respective electric field vectors E parallel and 180 degrees out of phase with one another. The electric field of each of the two portions of the wave energy is then progressively deformed to assume the familiar circularly symmetric pattern of the TE -mode of the coaxial waveguide. in the final stage of reorientation. Finally after combining the two reoriented portions, the wave energy in the TE -mode of the coaxial waveguide and wave energy from the coaxial od of operation, together with further objects and advan-' tages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which several embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the invention.

Fig. 1 is a cross-sectional view of one embodiment of the duo-mode wave energy feed in accordance with this invention;

Fig. 2'is a cross-sectional view taken along line 2.2 of the duo-mode wave energy feed of Fig. 1;

Fig. 3 is a three-dimensional view of the evolute of the duo-mode wave energy feed of Fig. 1;.

Fig. 4 is a three-dimensional view of an alternate embodiment of the input portion of the duo-mode wave energy feed of Fig. 1; and I Fig. 5 is a three-dimensional exploded fragmentary view of the duo-mode wave energy feed of Fig. 1 showing the orientation of the electric field vector in progressive stages.

Referring now to the drawings and particularly to Fig. 1 thereof, there is shown one embodiment of the duo mode wave energy in accordance with this invention wherein there are sequentially coupled to one another a dividing means such as the hybrid T 10, an electric field reorientation means 12, and a combining means 14.

The hybrid T 10 has a sum arm 20, a difference arm 22 and two symmetry arms 24 and 26 respectively, and is adapted to propagate wave energy in the dominant TE -mode of the rectangular waveguide. The difference arm 22 is coupled to a rectangular input waveguide not shown in the drawing. Wave energy supplied to thediiference arm 22 from a rectangular input waveguide is coupled to the two symmetry arms 24 and 26 in equal proportion and of opposite phases as is well known in the art.

The electric field orientation means 12 essentially comprises anevolute 28 surrounded by a cylindrical housing 30 and abuts against a circular end-plate 32 which is provided with openings to permit wave energy from the symmetry arms 24 and 26 to enter the field reorientation means 12. The evolute 23 comprises essentially a pairof identical flutes 34 and 36 rigidly fastened to the outer conductor 38 of a waveguide 40. The outer conductor 38 and the cylindrical'housing 30 also form a coaxial waveguide which is radially divided by the flutes 34 and- 36 into two waveguides 42 and 44 which progressively change in cross-section from substantially rectangular to waveguide 52. The coaxial waveguides 40 and 52 are of equal dimension and actually form a single continuous coaxial rwaveguiden Theinner; conductor 54. extending throughout the whole. l6l'1gth Ofullh6';VOlUtQ 23-and the splineafiltendtmay be-supported by teflomwashers 56 and VSSh- IThe-Duter conductor 50 and thecylindrical housing 30 may besregarded as forming a coa'xial waveguide which is .an extension ofthercoaxial. waveguide formed by the. outencondnctor 38- and. the cylindrical housing 30.. The radial vanes or fins 48 divide this waveguide into a plurality of .sectoral. waveguides each capable of propagating wave energy in the. TE -mode. The'spline filter 46 is;.terminated by tapering, the radial, fins 43 from the, end portion 60 ofthe outer conductor 55) graduallyin the formof a trailing edge-62 to thecylindrical housing 30. In this-,rnannenthe trailing edges 62 of..the. spline filtendti .torm. an. inverted cone and. provide. for awave energytransition' from the coaxial waveguide 52 .to, a new. .coaxial Waveguide 64 formed the inner conductor 54and.thecylindricalhousing 30. In other words .thetrailing edges; 62 ofythe spline'filter 4s provide .a smooth wave/energy.-.transition between two coaxial waveguides. of different. dimensions.

. Fig. 2 is aL-cross-sectional end. view takenalong the line 2720f 'Fig. .1..-and. shows with greater particularity thedetails ofathe endplate 32... The end plate 32 is provideduwithytwo rectangulanopenings 7G and 772 to which arelcoupledthe symmetry. arms .24and26 of the hybrid T 10, respectivelyv The openings 70 and 7?. become one of the end portions of theprogressively.widening waveguides definedfby the-Hflutes .34 and 36, respectively. T he opening 74.at the ,center loflthe end plate 32 permits access to the coaxial waveguide 49,10; which is coupled a coaxial input Waveguide 76.shown in ,Fig. Fig. 2 further shows'the direction and .the relative phase. of the electric field vectors E of the; wave ener y upon entering the. electric .field reorientation means 12.

Fig; 3is athree-dirnensiopalview.ofthe evolute 23 of fthe duo-'modewavefenergy feed of,,Fig.-.l,showing with greater particularity its geometrical configuration. Two flutes 34 and 36 are attached to outer conductor'38 of the coaxial waveguide 40. Thesectoralspace lying between the flutes 34' and 36 provides theprogressively widening waveguides42 and 44 defined by the side Walls of the. flutes 34 and 36, t he outer conductor 33 and the cylindrical housing 30 shown. in Fig. 1. The progressively widening waveguides 42 anddl have ,a. substantially rectangular cross-section at the end portion, 82 and a substantially semi-circularpress-section at the end portion 84.. The changeof waveguide cross-sectionfrom oneendportion toithe other end portion :is gradual and smooth and not critical. The length of the evolute 12 is determined solely by. considerations of how perfect a transformation isfldesiredh Shorter evolute length requires, a steeper-shape ofthe flute walls and greater im pedance mismatch, which is attended with the possible generation of higher order IDOClS.'.

Fig..14 is athree-dimensional view of a, ditferent embodiment of the dividing-means which may be used instead of the hybrid junction 16 of Fig. l. A rectangular waveguide. 90 is, coupled to a :Y-type :power vdivider 92 which :hastwo output waveguides 94 and 96, respectively, -The :outputwaveguides ,94 and .96 are each twisted through an; angle .of; 9.0 degrees so that a relative rotation of -180 degrees-results. The. output waveguides 94 .and 916 may bejoined to the .end plate 32 in the samefimanner as thesymmetry arms 24 and 260i Fig. l. The. rectangular waveguide 90 may be coupled to the rectangular input waveguide not shown in the drawings. Fig. 4also;shows the relative orientation and phase of the-electric field vector E atthe input endzot the waveguide 96 andat the output ends of waveguides 94 and 9.6, I'fiSPGCIlVfiiY. 1 Wave energy which enters .the rectangular waveguide 90 is split. upinto two equal components by the power divider 92 and rotated 180 degrees 4 with respect to one another in the twisted output waveguides 94 and 96.

Fig. 5 is a three-dimensional exploded view of the duomode wave energy feed of Fig. 1 showing in progressive stages the reorientation or deformation of the electric field vector E, and is included to aid in the explanation of this invention. The electric field vector is shown on the drawings as a heavy line with an arrow indicating its relative phase. Wave energy from a rectangular input wave-guide which is coupled to the difierence arm 20 of the hybrid T it) is split up into two components of equal magnitude which are degrees out of phase with one another. The perspective view or" the end plate 32 shows the relative orientation of the electric field vectors E in the symmetry arms 24 and 26 respectively. A coaxial input waveguide 76 propagating the principal TEM-mode is coupledto the opening 74 of the end plate 32 whichin turn couples to the coaxial. waveguide 40. Wave energy enters. progressively widening waveguides 42 and 44 in the TE -mode from the symmetry arms 24 and 26 .wherein the electric field vector E changes its direction from that ofa straight lineto that of a semi-circle which semi-circle is complete when theend portion of the evolute.28 is reached. The spline filter 46 freely passes wave energy in the TE -mode of the coaxial waveguide but no higher order modes and therefore eliminatev all higher. modes which, may be generated in the progressively widening waveguides 42 and 44 due to impedance mismatch. After transmission through the spline filter 46 a pure TE -mod is obtained in the output means 16.

The principal TEM-mode propagated through the coaxial waveguide 40 and 52 is expanded or exploded with the aid of the tapered or trailing edges 62 of the individual vanes 48, of .the spline filter 46. As mentionedbefore this expansion or explosion of. the outer conductor. Shinto coincidence with the cylindrical housingfill-is similar to a conical transition between two coaxial .waveguides. of different diameters. After] the .cxplodingof ;-the-,.wave energy in the principal TEM.-mode..an intermixing of the exploded wave energy with thewave energy inlthe IE rnode takes place. Inthis.manner the. coaxial output waveguide 64 provides wave energy. having. a. combination ofthe principalrTEM-mode and the TE -mode of the coaxial waveguide. v

HTheduo-mode-wave energy .feed in accordance with this invention therefore provides at its output end the principalTEM-mode and tl1e.T-E -mode of the coaxial waveguide intermixed withcne another. 'The. inputend of the duo-mode wave energy iscoupled-to a'rectangular input'waveguide adapted to supply wave energy in the TE -mode and to a coaxial inputwaveguide adaptedto supply, wave energy in theprincipal: TEM-mode.- The wave-energy mode transition from the TE -mode of the rectangular waveguide to the TE -rnode ofthe coaxial waveguidetaking place within the duo-mode wave energy feed is a unity. transition and consequently this feedmay be employed when high power transmission and broad band operation is required.

Whatis claimedis-z t w u..l."A duo-mode wave energy feed having a coaxialoutputawaveguidemember adaptedto providea predetermined combination of wave energy in-thelTE -mode and the TEM-mode and comprising dividing means for dividingwave energy. in the dominant TE rectangular waveguide. modeu'ntol two :substantially equal :portions and includingameansto impart a 180 degree relative phase shift-.ibetwee'n .said iportions; electric .field orientation meansicoupled' to'saidi dividing means for combining said two portions of wave energy to.form-the TE -rnodepf a coaxial waveguide;.-a coaxialinput waveguide having an outer: and an inner :conducto'r; a spline filter within-"a cylindrical housinghaving radial vanes extending from said, outenconductor and coupled -to'- said -electric field reorientation means, one end of said vanes-=having-a trailing edge extending beyond said outer conductor and effectively expanding said outer conductor into coincidence with said cylindrical housing, said inner conductor and said outer conductor stisequent to expansion and coincidence with said cylindrical housing defining said coaxial output waveguide member.

2. A duo-mode wave energy feed having a coaxial output waveguide member adapted to provide a predetermined combination of Wave energy in the TE -mode and the TEM-mode and comprising: dividing means for dividing wave energy in the dominant TE rectangular waveguide mode into two substantially equal portions and including means to impart a 180 degree relative phase relation between said portions; electric field orientation means coupled to said dividing means for combining said two portions of Wave energy into the TE -mode of a coaxial waveguide; a coaxial input waveguide adapted to provide wave energy in the TEM-mode having an inner and an outer conductor, a cylindrical housing coaxially surrounding said outer conductor and defining a coaxial waveguide, said coaxial waveguide being coupled to said electric field reorientation means; and expansion means coupled to said outer conductor for coaxially expanding said outer conductor into coincidence with said cylindrical housing, said expanded outer conductor and said inner conductor defining said coaxial output waveguide member.

3. A duo-mode wave energy feed having a coaxial out-. put waveguide member adapted to provide a predetermined combination of wave energy in the TE -mode and the TEM-mode and comprising: dividing means including a rectangular input waveguide for feeding wave energy in the TE -mode into said dividing means, said dividing means adapted to divide said wave energy in the TE mode into two substantially equal portions, said dividing means including an element for separately and oppositely rotating each of said two portions of wave energy through an angle of 90 degrees; electric field reorientation means responsive to said rotated portions of wave energy coupled to said dividing means and adapted to combine said two rotated portions of wave energy to provide the T E -mode of the coaxial waveguide; a coaxial input waveguide having an outer and an inner conductor and a spline filter within a cylindrical housing having radial vanes extending from said outer conductor coupled to said electric field reorientation means, one end of said vanes defining an inverted cone and effectively exploding said outer conductor into coincidence with said cylindrical housing, said coaxial input waveguide adapted to feed wave energy in the TEM-mode through the central portion of said spline filter, said inner conductor and said outer conductor subsequent to expansion and coincidence with said cylindrical housing defining said coaxial output waveguide member.

4. A duo-mode wave energy feed having a coaxial output waveguide member adapted to provide a predetermined combination of wave energy in the TE -mode and the TEM-mode and comprising: a rectangular Y-type power divider having two rectangular output ports; two mirror image rectangular waveguide sections each twisted in opposite rotational sense through an angle of 90 degrees and each coupled to a different one of said output ports whereby said mirror image waveguide sections provide wave energy in the dominant TE -mode having their respective field vectors 180 degrees out of phase with one another; a coaxial input waveguide having an outer and an inner conductor and adapted to provide wave energy in the TEM-mode; an evolute contained within a cylindrical housing having two radial flutes of progressively changing cross-section extending from said outer conductor, the surfaces of said outer conductor, said housing and said flutes defining two substantially identical progressively widening waveguides whose cross-sectional area changes smoothly from substantially rectangular to substantially semi-circular, said two progressively widening Waveguides each coupled to a dilferent one of said mirror image waveguide sections; and a spline filter within a cylindrical housing having radial vanes extending from said outer conductor coupled to said evolute, one end of said vanes defining an inverted cone and effectively exploding said outer conductor to coincidence with said cylindrical housing, said inner conductor and said outer conductor subsequent to explosion and coincidence with said cylindrical housing defining said coaxial output waveguide member.

5. A duo-mode wave energy feed having a coaxial output waveguide member adapted to provide a predetermined combination of wave energy in the TE -mode and the TEM mode and comprising: a hybrid T having a diiference arm for feeding Wave energy into said hybrid T and two symmetry arms for providing substantially equal portions of wave energy in the TE rectangular waveguide mode having a degree out of phase relationship between respective electric field vectors; a coaxial input waveguide having an inner and an outer conductor and adapted to provide wave energy in the TEM-mode; an evolute contained within a cylindrical housing having two flutes of progressively changing cross-section extending from said outer conductor, the space defined by said outer conductor, said housing and said flutes providing two progressively widening waveguides whose cross-sectional area changes progressively from substantially rectangular to substantially semi-circular, said two progressively widening waveguides being coupled to a different one of each of said two symmetry arms; and a spline filter within a cylindrical housing having radial vanes extending from said outer conductor, one end of said vanes defining an inverted cone and effectively bringing said outer conductor into coincidence with said cylindrical housing, said inner conductor and'said outer conductor subsequent to coincidence with said cylindrical housing defining said coaxial output waveguide member.

6. A duo-mode wave energy feed having a coaxial output waveguide member adapted to provide a predetermined combination of wave energy in the TE -mode and in the TEM-mode, said wave energy feed comprising: a coaxial waveguide having an inner and an outer conductor and adapted to be excited in the TEM-mode, a cylindrical housing axially surrounding said outer conductor, a pair of flutes of progressively changing crosssection extending radially from one portion of said outer conductor and longitudinally dividing the space between said outer conductor and said cylindrical housing into two Wave propagation paths each having a cross-sectional area which changes progressively from a substantially rectangular area defining the input end to a substantially semi-circular area forming the output end of said waveguide propagation paths, feed means coupled to said input end of said propagation paths and adapted to feed each of said wave propagation paths an equal amount of wave energy in the TE rectangular waveguide mode whose electric fields have a 180 degree relative phase relation with respect to one another, a set of radial vanes extending from another portion of said outer conductor and extending to said cylindrical housing, said vanes each having trailing edges which define the surface of an inverted frustrum of a right circular cone, said trailing edges gradually exploding said outer conductor into coincidence with said cylindrical shell, the inner conductor of said first coaxial waveguide and said exploded outer conductor defining said coaxial output waveguide.

References Cited in the file of this patent UNITED STATES PATENTS 2,231,602 Southworth Feb. 11, 1941 2,656,513 King Oct. 20, 1953 2,691,731 Miller Oct. 12, 1954 

